/Engine/Source/Runtime/RHI/Public/DynamicRHI.h
Watch out for OutData to be 0 (can happen on DXGI_ERROR_DEVICE_REMOVED), don't call RHIUnmapStagingSurface in that case.
void RHIMapStagingSurface ( [FRHITexture](API\Runtime\RHI\FRHITexture) * Texture, [FRHIGPUFence](API\Runtime\RHI\FRHIGPUFence) * Fence, void *& OutData, int32 & OutWidth, int32 & OutHeight, uint32 GPUIndex )